This invention pertains to microwave antennas, and more particularly is concerned with microwave antennas excited by planar surface waves.
Many communication systems require a flat, planar, low profile aperture antenna that can be easily conformed to an existing structure such as the skin of an aircraft, or concealed in a flat surface as required in covert communication system applications. In the past, monolithic microwave integrated circuit (MMIC) phased arrays have been used for such applications because they provide a low profile aperture. The usual reasons for using a phased array such as high speed beam scanning and multi-beam/multi function requirements do not exist in these applications.
There are two major disadvantages to a phased array technique for such applications it is very costly since the amplitude and phase at each point in the aperture is controlled discreetly; and the upper frequency limitation of the MMIC phased array technology is unacceptable for communication systems in which the need for greater bandwidths requires operation in the submillimeter bands.
Classical surface (slow wave) and leaky (normally fast wave) antenna structures are end fed, typically, by a microwave horn. Planar (two-dimensional) apertures are constructed by physically paralleling individual one dimensional travelling wave elements. They have several disadvantages: the antenna beam is normally in or close to the end-fire direction; the beam direction scans with frequency; and, horn launchers radiate directly resulting in degraded lossy antenna pattern characteristics.
Though it is theoretically possible to make a broadside leaky wave antenna at one frequency by introducing appropriate phase reversals along the element, it is difficult if not totally impractical at EHF.